1. Field of Invention
This invention relates to antenna assemblies for hand held radio frequency transmitters or receivers, and more particularly to antenna assemblies for communication devices such as cellular telephones, PCS devices, and the like.
2. Description of the Related Art
Various antennas have been proposed and implemented for radio frequency communication devices such as cellular phones, PCS telephones and the like. Antennas have also been proposed and developed for other applications, for example, U.S. Pat. No. 5,677,698 shows a slot antenna arrangement for portable personal computers. Prior antennas for radio frequency transceivers for telecommunication devices such as cellular telephones and PCS devices have had significant limitations including limited signal range, limited directionality, significant radio frequency radiation output to the user, significant multipath interference, and other related performance limitations.
Accordingly, it is the primary object of this invention to provide an improved antenna for communication devices including hand-held radio frequency transceivers such as cellular phones and PCS devices with improved directionality, broadband input impedance, increased signal strength, and increased battery life. The present invention reduces radio frequency radiation incident to the user's body and reduces the physical size requirements for a directional antenna used on communication devices. Other benefits include a reduction in multipath interference, an increased front-to-back ratio, and improved peak gain. The antenna assembly of the present invention may be integrated into the housing of a cellular transceiver, for example, at the rear portion of a cellular telephone, and is accordingly less susceptible to damage during normal operation.
In general, wireless communication devices, and hand held cellular telephones in particular, use external whip antennas which radiate nominally omnidirectionally. Minimal reduction in transmitted RF energy toward the user's head is provided. As a consequence, typical specific absorption rates (SAR) values of 2.7 mw/g at 0.5 watts input are realized. The external whip antenna is also susceptible to damage and misalignment. Gain of the whip antenna is typically in the range of -5 to +1.5 dBi.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.